.root{
    position: relative;
    z-index: 3;
    height: 40px;
}

.mask{
 position: fixed;
 z-index: 2;
 left: 0;
 right: 0;
 top: 0;
 bottom: 0;
 background-color: rgba(0,0,0,.5);   
}

.content{
    position: absolute;
    width: 100%;
    z-index: 3;
    background-color: #fff;
}